Electric musical instrument



Sept 19, 1961 w. c. WAYNE, JR 3,000,252

ELECTRIC MUSICAL INSTRUMENT Filed Oct. 9, 1953 6 Sheelzs-Sheerl 1 MODUIATO'RF- 'FILTER Sept. 19, 1961 w. c.`wAYNE, JR 3,000,252

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ELECTRIC MUSICAL INSTRUMENT Filed Oct. 9, 1953 6 Sheets-Sheet 3 Sept- 19, 1961 w. c. WAYNE, JR 3,000,252

ELECTRIC MUSICAL INSTRUMENT Filed Oct. 9, l953` 6 Sheets-Sheet 4 Sept. 19, 1961 Filed oct. 9, 1953 ONE.' OCT/IVE W. C. WAYNE, JR

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United States Patent Ofice 3,000,252 i ELECTRIC MUSICAL INSTRUMENT William C. Wayne, Jr., Cincinnati, Ohio, assignor to The Baldwin Piano Company, Cincinnati, Ohio, a corporation of Ohio Filed Oct. 9, 19153, Ser. No. 385,138 l`17Claims. (Cl. 84-1.01)

My invention relates generally to electric musical instruments of the type wherein electric oscillations corresponding in characteristics to tones of the usual equallytempered musical scale are produced by a set or series of sources of such oscillations, selected by one or more keyboards, combined and/or modified for various tone colors and converted to sound -by electro-acoustic means.

ln particular, my invention concerns methods and systems for creating, from such instruments wherein a single set only of sources of such oscillations is present, ensemble and other efects Which heretofore have been obtainable only from an instrument having a plurality of sets of sources. The ensemble or chorus effect is similar to that of a celeste tone color in a pipe organ, which is produced when each organ key simultaneously sounds two or more pipes intentionally tuned to slightly diierent pitch.

By way of general background for a better understanding of certain principles underlying my invention, it has been pointed out by Hammond et al. in U.S. Patent No. 2,498,367 issued lFebruary 21, 1950, that the richness of most musical tones may be greatly enhanced by the utilization of several tone generating sources, all of which sound simultaneously to produce a chorus effect. This eilect is commonly observed in orchestras where it is not unusual to see a relatively ,large number of musicians playing the same note on the same kind of instrument. The explanation of the resulting beauty ot' their composite tonality resides in the fact that the musicians inadvertently play at slightly dierent pitches. The result is an interesting and pleasing tonal undulation. If all the musicians were to play at exactly the same pitch, theV resulting eifect would be substantially identical to that produced by a single player save for a somewhat increased loudness due to the multiplication of the number of instruments. These inadvertent differences in pitch, While productive of a veryV noticeable change in quality, are actually very `Asmall, their v,mutual deviation factor being a fraction of a percent. Apparatus for producing similar chorus effects have also been provided in organs, accordions, harpsichords and the like. For example, as pointed out above, the celeste stop on a pipe organ will bring simultaneously linto play two or three ranks of pipes, so that when one organ key is depressed, two or three pipes of slightly different pitch will sound. Quoting Hammond further: That these chorus effects arel beautiful cannot be denied. yTheir eiect musically is of fundamental vimportance in orchestras, keyboard instruments', and choruses of voices. Y

`In an electric organ-'in which a single set of generators of electric oscillations (corresponding in characteristics respectively to the musical -tones,produced), and partcularly in such an organ wherein generators in ,the set are interlocked as to frequency relationships, the ensemble Y of the music produced lacks lthe musically desirable chorus effect described above. To overcome this fact some workers in the art have followed the", expensive and expansive practice of employing two or more contplete sets ofA generators and of deliberately detuning them slightly, note-for-note, from the nominal pitch to accomplish a chorus effect. Although this is analogous, of course, to pipe organ practice, wherein, as pointed out above, several pipes for each note of a celeste tone color are sounded simultaneously, it is nevertheless an Patented Sept. 19, 196i elaborate and uneconomical procedure in view of methods and means such as I disclose herein. Furthermore, if the frequencies of the generators in a multiple-set instrument are not locked together in some way, the problem of individual tuning of each source becomes burdensome. Consequently, my invention has for an important object the teaching of a simple, practical and relatively inexpensive method for producing a celeste effect in an electric musical instrument having only one set of sources of electric oscillations respectively corresponding to the notes of the usual equally tempered musical scale.

Another important object of my invention is to provide an electric musical instrument having tone colors simulating those of celeste ranks in a pipe organ.

A further object is to provide an instrument as in the preceding object, in which the fundamental and harmonic frequency components of each tone are phase and amplitude-modulated at sub-audio rates which progressively increase with pitch.

It is believed that certain ancillary objects of my invention may be comprehended more readily following a delinition of certain terminology to be used herein. The term footage denotes pitch range with respect to normal pitch. Usually, in pipe organ practice, 8 ft. pitch is the normal for a given manual key, while 16 ft. pitch is the normal for a pedal key. The terms were derived originally from thel lengths of pipes. So, for example, if a stop-tab for a manual tone-color designated as Diapason 8 is chosen, then when a manual key is depressed, the pitch of the note produced Will be the normal for the key. lf, then, a Flare 4 stop is selected, the pitch of the note produced by the same key will be an octave above the normal (8 ft.) pitch. Similarly, a 2 ft. stop will produce a note two octaves above the 8 ft. pitch or one octave above the 4 ft. pitch. The selection of a l6 ft. tone-color will result in a tone an octave below the S ft. tone.

Now, in `a pedal keyboard, 16 ft. is normal pitch, so a 32 ft. tone-color will produce a tone one octave below the normal (16 ft.) pitch.

A further object, then, of my invention is to provide an improved simple method and means for obtaining 32 ft. tone-colors from a pedal keyboard in an electric organ without the need for actual sources of oscillations for the lowest octave compass of notes.

A still further object is to provide means for producing in an electric organ at least one mixture tone-color (that is, one of combined footages, such as 4 ft. and 2% ft. for a. given stop-tab) Without the necessity for an extra deck of key switches for certain additional footages.

Another important object is to provide an improved simplied circuit means for an electric organ whereby celeste, mixture and 32 ft. tone-colors may all be produced from a single set of generators fewer in number than the individual notes to be produced and with fewer key switches than have heretofore been necessary.

These and other objects which may be set forth hereinafter or will bev apparent to one skilled in the art upon reading thesespeci'cations, I accomplish by those circuits and arrangements of parts of which l shall now set forth exemplary embodiments. Reference is made to the accompanying drawings, wherein:

FIGURE l is a block diagram illustrating certain basic principles of my invention;

FIGURE 2 is a simplified schematic diagram illustrating a basic circuit of my invention;

FIGURE 3 is a schematic diagram showing a further principle of my invention; y

FIGURE 4 is a schematic .diagram illustrating an alternate to the system of FIGURE 3;

1FIGURES 5a and 5b are a simpliiied circuit diagram of an analytic type electronic organ employing the teachings of my invention as applied to a manual keyboard;

FIGURE 6 illustrates a modication in the circuit of FIGURES a and`5b; YFIGURE 7 is a chart showingrvarious relationships between 'the components of celeste or chorus voltages produced in accordance with my invention; r

FIGURE 8 is a simplified circuit diagram of an analytic type electronic organ employing certain teachings of my invention which, in this instance, are applied to a pedal keyboard; and

VFIGURE 9 is a chart showing the relationsh1ps between unison and celeste frequencies throughout more than one octave. v 'f The fundamental concept The fundamental concept of myinvention is based upon the inherent out-of-tun-eness of certain musical '1ntervals in the equally-tempered musical scalegi-n which adjacent half-tones are related in the -ratio of si/11 1 For example, the tempered ifth is not a perfect or integral ratio, as is the fifth in the just scale, the former being in the ratio of (1.4983:1 when expressed as a decimal ratio), while the latter ratio is 1.5000:1 (or the integral ratio of 3:2). l Another example is the tempered fourth, which is the ratio of whereas the perfect fourth is in the ratio of 4:3, another integral ratio.

`Broadly, according to one aspect of my invention, I combine, for each note to be produced, ya pair of periodically oscillating voltages which may be harmonically complex in nature (in order to correspond in characteristics to harmonically complex musical tones) whose fundamental frequency components correspond respectively .to one of the above-mentioned certain intervals in the equally-tempered musical scale, the combination being carried out by a modulation process in such a way as to producesum-frequency and/or dilference-frequency voltages having, if the original two voltages complex, a series of harmonically related components based on the fundamental frequency of the difference-frequency voltage so produced. For example, if a voltage corresponding to a tone C4 (261.626 c.p.s.) is combined as described above with a voltage corresponding to a tone G4 (391.995

Case I-Amplitude Modulation (nonlinear combination) Let em be the amplitude modulated wave produced by the non-linear e carrier wave whose amplitude is made proportional to the instantaneous value of the moth ulating signal Wave e2 through the action of the non-linearl device.

Assume and According to the above definition of amplitude modulation, E1 is a.

or, em= term (1) [kEg cos egt] cos wit v term (2) +E1 cos alt Example rs 1 c. .s. Inspection shows that em is a wave made up of two terms:

Suppose that f1 (the carrier) is 101 c.p.s. andfz (the modulating signal A p frequency) (l) A wave of frequency 101 c.p.s. whose phase reverses twice a second and whose amplitude variesv cyclieally twice a second, thus, the

average value over an integral cycles 1s zero.

multiple of two amplitude beat (2) A wave of frequency 101 e.p.s. of constant amplitude and phase.

c.p.s.), the dilference-frequency will be 130.369 Q .p.s. (corresponding nearly to a note vC3 at 130.813 cpa-an oe-` tave below C4) with harmonic frequency components depending upon the existence and relative strengths of the harmonic components of the C4 and G4 voltages combined, las will be described in detail hereinafter. As will be pointed out'below in the discussion of FIGURE 2, some celeste effect is produced-as :the result'of certain modulation products differing slightly from components of one or both of the voltages applied to` the Vmodirlator'. However, in order to more nearly simulate a pipe organ celeste, wherein the fundamental .and each harmonic of one pipe beat with the fundamental and the respective harmonic of another pipe, I may, as another-step of my invention, linearly combine this derived voltage Vwith another voltage harmonically related to one of the voltages of the original pair and which, at the same time, is close in frequency to the derived voltage. This unison voltage may, for example, be provided by means of frequency division from one of the voltages in the original pair.

The block diagram of FIGURE 1 illustrates these basic stepsl of my invention. Voltages corresponding to notes C4 and G4, derived from `sources 2 and 4,v respectively, are fed to-a modulator `6 of a type subsequently to be discussed. The derived voltage at a fundamental fre-A quency of 130.369 c`.p.s. is fed to an adding network 8 along with a unison voltagea't 130.813 cps. which may be derived by frequency division in a suitable frequency divider 10. Circuit details will be described in connection with FIGURES 2, 3, l4, 5a, 5b, and 6.

vThis linear addition in the network 8 yields a complex voltage whose magnitude is characterized by slow undulations in amplitude, commonly called beats, that occur'in its fundamental and harmonics (if any are present) as well as a complete phase reversal once each beat cycle so that, when converted to soundV in an electro-acoustic system lof the usual type, a celeste or chorus effect is produced. The phase reversals occur at such a low repettion frequency that they are inaudible. Therefore, the listener senses only the amplitude modulation although mathematical analysis shows that the beat wave has both phaseand amplitude-modulation characteristics.

In order to clarify amplitude modulation and beats, two processes which are both involvedl here in the production of celeste, a mathematical analysis of each follows, which includes specific examples and discussions of the output waves.Y

The relation between a wave having amplitude modulal Oase II-Beats (linear combination) Let er, be the beat Wave produced by the linear combination of e1 and e2. Assume e1 1s the unison voltage and e2 is the derived voltage. The angular velocity w1 slightly exceeds w Y eb= [2E'2 ccs (wlgwOt-l cos (w12*"2 t+[E1-E2] cos w1 If fo is the celeste tone audio frequency Iffb is the beat sub-audio frequency Observe that terms k(1) are identical in both cases. Terms (1) include the combined upper and=lowerlside bands of frequencies 102 c.p.s. and 100 c.p.s., respectively. Thus, it can be seen that the difference between Case I and Case II occurs in the frequencyinequality of the two terms (2). Because of the phase reversals noted, no'electrical power can be supplied at a frequency of 101 c.p.s, in either case from terms (1), but can be supplied by term (2) Case I.r However, useful celeste output is obtained at 101 c.p.s. from term (l), Case II since the overall hearing system does not detect the sub-audio frequency phase reversals. Identical waves may be obtained involvi-ng only terms (l) from both cases if terms (2) are eliminated. This is accomplished in Case I by using a balanced modulator which suppresses the carrier, i.e., term (2), and, in Case II by choosing E1 to equal E2 in amplitude. The number ofrbeats per second heard by an observer in the example, Case II, is two per second which, at first glance, would not appear to be in accord with the mathematical value of Again, this is a manifestation of the fact that (at subaudio beat frequencies) the overall hearing system regards one beat wave just as the following beat wave, although the latter has undergone a complete phase reversal. Mathematically, only one complete beat cycle per second occurs but practically, the observer responds to two complete beat cycles per second. The usual formula to be found in physics textbooks that fb is f1 minus f2 should be qualiiied accordingly.

In accordance with the foregoing, if the derived voltage of 130.369 c.p.s. is linearly combined with a voltage corresponding to C3 (130.813 c.p.s.) an exact octave below (or one-half the frequency of) C., of the original =1 c.p.s.

pair, an audible beat rate of .444 c.p.s. (130.813-

130369) will result.

As a step of my invention alternate to the one just described wherein voltages are linearly combined before conversion to sound, I may convert the derived voltage to sound in one appropriate electroacoustic system and simultaneously convert to sound in another electroacoustic system another voltage harmonically related to one of the voltages of the original` pair and which, at the same time, is close in frequency-to the derived voltage, the linear combination being accomplished in the air or medium in which the sound is produced. The' procedure will be described in detail-in-conncction with FIGURES 4 and 6. Before proceeding with a detailed description of my invention I shall discuss `pertinent acoustical principles involvedherein. l'

Background and priorart `By way of background, to distinguish my invention from the prior art, it has longbeen knownthat there can .be created in the ear ar subjective tone of a given frequency even though physically there arel no sound waves of that frequencypresent (Seashore, Psychology of Music, McGraw-Hill, 1938.). -Forexample, if pure tones`having frequencies of 400, 600,j800, etc. cycles per second are sounded simultaneously, the sensation of -hearing a 200 c.p.s.,note will be had Vby the listener. This phenomenon has been employed by pipe organ designers, who produce the effect of a very low note (which, to produce physically, requires a very long pipe) by sounding two smaller pipes whose pitch dierence is equal to one-half the frequency of the lower of the two pipes. The subjective tone thus produced has been called a resultant or differential tone (Audsley, t Art of `Organ Building, Dodd-Mead, 1905).4 A currently manufactured electronic musical instrument employs this phenomenon in producing. each bass note in its lowest octave by feeding to a loudspeaker system the v yalgebraic Sums (obtained from electrically linear adding networks) of two oscillating voltages related as to fund damental frequency by an interval corresponding to a fifth in the musical scale (a ratio of about three to two in the equally-tempered scale), the upper of the two voltages being reduced as to amplitude. The frequencies are near enough to a 3:2 ratio that the instrument can produce to a moderate degree the subjective e/ect of a series of low notes, for which in the instrument, there are actually no oscillating electric voltages corre- `sponding in frequency to the low notes.

In one prior art circuit, the electric oscillations produced by two generators correspond in fundamental frequency, for example, to the notes G and D, respectively, and are combined at a connection after passage through two decoupling resistors, respectively.v The reresistance of one resistor is several times that of the other resistor, so that the tone produced by the system will not contain an excessive amount of the D frequency, which would mask the subjective effect, (produced in the ear of the listener) of the G frequency an octave below that of the G frequency produced by the generator. If the key switch connecting the junction to ground is open, the algebraic combination of the oscillations produced by the generators is permitted to pass along through a resistor, through a lter system, an amplification system and an electroacoustic system. In this known type of instrument the combination of the oscillations from the two generators is strictly a linear, algebraic one and electric oscillations corresponding in fundamental frequency to the note G below that produced by the first generator are not actually present in the circuit.

Another prior art system (U.S. Patent No. 2,561,349 to C. W. Earp) starts with a source of electric oscillations which are passed through two separate paths to a modulator to which, in series, are connected a filter systern and electroacoustic projector means. In one of the two paths just mentioned is a frequency divider and a filter.

The frequency divider divides by integral powers of 2, and the modulation output contains adifference-frequency component, which is converted to sound to produce a lower frequency tone which is an integral submultiple of the fundamental frequency of oscillations from the source, the purpose being to achieve a loudness level which is directly proportional to the strength of the original input oscillations. The narrowest `common ground of similarity between Earps teachings and mine is that of feeding two audio frequency components of the order of one-half of the frequency of one of the input voltages. From this common ground in the art, whichis new neither'with Earp nor with me so far as basic circuitry is concerned, Earp, of necessity uses an integral frequency divider to provide one of his input oscillations so as to obtain a frequency which is an integral submultiple of the frequency of one lof the original oscillations. I have found that feeding to a modulator a pair of voltages related in frequency as certain intervals of the equally-tempered scale will produce modulation product voltages usable either with or without algebraic combination with other voltages to accomplish chorus and other effects. It will be seen that oneV of the basic diiferences between Earps system and mine is that I purposely produce a lower frequency tone which is not integrally related (as to frequency) to one of the original oscillations.

It should be pointed out that neither of these two prior art systems provide a chorus effect in which the effect of two or more notes of nearly the same pitch are produced simultaneously.

Basic circuit of my invention scale from two generators l33 andi 35 through twovdecoupling resistors 37 and 39, respectively, and ,two key switches` 41 and 43, respectively, to a square-law modulator 45. For the purpose of this disclosure, a square-law modulator may be defined as a circuit'element whose current-voltage characteristic is such that the `current through the element depends on the second power or square of the impressed voltage. `The output of themodulator 45 maybe fed through a tone-color filter.53," selectively coupled by means of a stop-switch 54 to :an output system, which may comprise an audio amplifier 55 and an electroacoustic translator 57, for conversion ofthe tone voltages to sound. The tone-color filterl 53 may be of ythe low-pass, high-pass, band-pass or otherjtype known in the art. Examples lare shown. in KockfPatont No. 2,233,948.

As will be apparent to one skilled in themodulation art, the output tones ofthe system, as mentioned briefly above, will be phase and amplitude-modulated a-t subaudio rates. This cornes about Yby the factthat, the respective fundamental and harmonic frequencies of the generators 33 and 35 larenot integrally related; thus modulation products exist in the'output which differ in frequency by small amounts from the originally combined-voltages, which are also present in the output, unless they have been balanced out. l ForV example, assuming that the two generators 33 and 35 produce tone voltages having fundamental lfrequency components corresponding to notes C4 (261.626 c.p.s.) and G4 (391.995 c.p.s.), halvng third harmonic components of 784.878 c.p.s. and 1175.985 c.p.s., respectively, the third harmonic difference frequency is 3491.107 c.p.s. It will be noted that this differs from the G4 fundamental by (391.995'-391.107 c.p.s.) or .888 c.p.s., a sub-audio frequency.

As will be described subsequently in connection wit-h FIGURE 7, I may employ the basic teachings of IFIG- URE 2 to produce 32 ft. tones from' an instrument having no actual generators of tone voltages at the 32 ft. pitch. However, for producing the most desirable'celeste type tones, I prefer, as mentioned previously, either to linearly combine with the modulation product voltage another voltage harmonically related tol one ofthe originally combined voltages, or to carry out `in air the combination of a modulation product lwave with another wave harmonically related to one ofthe originally combined voltages. Regerring to lFIGURE 3 .for the basic exemplary circuit of Ysuch a combination, elements which correspond to those of FIGURE 2 havesimilar indicia.` Thus, in FIGURE3, I preferably feed oscillations correspondingto tempered fifths from two generators 33 and 35 `through suitable decoupling resistors 37 `"and 39 and key'switches 41and '4S-,respectively tou'afsquare-law modulator 45, as was the case in FIGUREZ.,k However, in FIGURE 3, mechanically interlocked to the vtwo switches` 41 and 43I is another key switch "41 which peri mits oscillations from athirdl generator 49, corresponding in frequency to a" note an octave Vbelow (exactly one-half frequency) that produced by the one generator 35 to pass through a decoupling resistor 51 to` be combined linearly Vor algebraically at the pointvSZwithlthe'" oatpatof the square-law modulator 45', for rvmodiiication, as desired by as tone-color lter system 53, a stop-switch 54, andtsub'sev quent t amplification and translationinto sound lby `an amplifier 55 and an electroacoustic device 57.

As is known in the electronic `arts,;the output of the modulator Y45`of lFIGURE 3y Will contain components Vwhose frequenciesare the sums and-differences, respectively, of those components ofthe Yinput-oscillatirms A strong component of the output willubethe'differencefrequency between the respective fundamentals of the two generators 33 and 35. Since these t-wo generators 33 and 35 produce oscillations corresponding in frequency to a tempered fifth respectively C4 (261.626 c.p.s.) and G4 `(391.995 c.p.s.) for examplee-their difent (130.369 c.p.s.) is near, but not equal to, the fren quency of the third generator 49, which, by the way of example, may be C3 (l30.813 c.p.s.) Aan exact octave bey low the IC4 of the generator 33. Thus, when the output of the third generator49 is combined algebraically with the output of the modulator II there are, physically in t'he circuit at 512,;tw distinct component voltages, which, when converted into sound by the proiector 57, produce the effect of two notes of Vslightly different pitch--cornparable to the result produced when two organ pipes, tuned slightly apart, are sounded simultaneously. It will be obvious to -one skilled in the art that the harmonics also of the oscillations combined at 52 will be slightly different in pitch, respectively, thus further developing'Y the similarity between the acoustic results of my system and that of the celeste tone color of a pipe organ. When the linear combination is to'be carried out in air the circuit of FIGURE 4 will preferably be employed.v

In this system the operation is the same as in `FIGURE 2, except that a second filter 53a stop-,switch 54a, amplifier 55a and electroacoustic system 57a are used to convert the voltage from generator 49 to sound. v

FIGURE 7 is a chart which shows the relationships between (a) components of two voltages corresponding in frequency to C4 and G4, which are used to obtain the modulation products and (b) the components of the voltage corresponding to C3, which voltage is linearly cornbined with the modulation products to obtain the celeste effect. Column I shows the frequency components in c.p.s. (cycles per second) of note C4 which, for the purposes of lillustration here, is assumed -to have four partials which are harmonically related, i.e. integral multiplesof the lowest or fundamental frequency component. Col-` umn II lists the components of the note G4, also having four natural harmonics. NColumns IlIaand` IIIb list the partials of the new modulation-produced Vvoltage C3 havingV component frequencies which are respectively equal to the differences and sums of the fundamental frequencies and the respective harmonics of G4 and C4. Column IV shows the fundamental and twenty-four nag tural harmonics of a complex voltage corresponding toa tone C3, exactly Vone octave below (i.e., one-half the frequency of) C4 of Column I. Columns Va andY Vb, respectively, show the arithmetic differences in c.p.s. between the respective fundamental frequencies andrespective harmonics of C3 and C3. It will be obvious to one` skilled in the art that these arithmetic differences will She the .beat rate between the respective components. Columns VIa and VIb show these respective differences or beat rates as percentagesof the Ycorresponding C3 cor'n ponents in Column IV. j

An analysis of the .chartof FIGURE 7 reveals several significant points regarding my invention.- lFirst, thepercentageofl339' (see Column VIa) 'not only is Vof the Lorderl of .4%, which, as pointed out by Hammond etal. in 'the aforementioned Patent No. 2,498,367', .is productive of a musically-,desirable chorunselfect,l but .falso-V is' a .constantpercentage throughout therange of boththarirnonic` and fundamental frequencies. Thiszfconstancy is Ytuning, of celeste ranks in 'a pipe organas pointed outby Ernest M. Skinnerin The Diapason of Julyv l; 1952 (page 287)- l f f analysis of'the chart of yFIGURE 7 shows www 9.. modulation, 'selecting only the lower sidebandV (Column Illa) for the celeste 'voltagez (l) The celestel effect dueto the upper-sideband (Column IIIb) is small because: l

(a) The percent difference is low-(068% a shown in Column VIb). f

(b) r[he higher frequency harmonic components of the upper-sideband are large in magnitude compared with the magnitudes of the natural higher frequency harmonic components as shown in Colu-mn IV. It is Well known that maximum cancellation is achieved-to give a beat wave envelope that cyclically varies from two times the maximum of the individual peaks torero-only when the peak values are equal. In pipe organ work, this means voicing the unison pipe from its out-of-tune celeste pipe to equal intensity as Well as the same timbre. Actually, a slight departure from this rule is made, to achieve a less obvious beat pattern and, therefore, a more artistic one, the two times peak to zero variation being too extreme. Accordingly, the celeste rank of pipes is usually a little less loud and a little less-harmonically developed than the unison rank.

(2) The characteristic (pointed out in lb above) o'r the large comparative magnitude of the higher harmonics of the upper-sideband would also give the wave form of the Iresultant tone an unusual ,amount of higher ord'er harmonics instead or the usual smooth tapering-off harmonicamplitude characteristic of la good musical tone.

(3) Intermodulation resulting in undesirable crossproducts (due to la modul-ation characteristic of higher order than two) would 'be further reduced by the use of single-sideband modulation.

In `lieu of Asingle-side'hand modulation, in a manner which will be described indetail i-n connection with FIG- URES 5a and 5b, I may employ low-pass filters to re duce he prominence of the higher order harmonics present in the upper-sideband (summation) products of the modulation process.

Exemplary instruments AA single-line diagram of the basic circuits of a complete musical instrument employing some of the teachings of my invention is shown in FIGURES 5a and 5b. The instrument is of the analytic type, such as that shown by Kock in U.S. Patent No.` 2,233,948,wherein complex oscillations corresponding to thenotes of a musical scale a-re Yselected through keyswitches, varied as to harmonic content `in appropriate lilter circuits and converted `to desired -tones byl an amplicationnand sound projection system. In the Kock-type .instrument octavely-related oscillations are key-switchedV respectively to headers which collect the oscillations for transmission to respective tone-color circuits, so that harmonically related voices may be produced simultaneously..y

In a similar manner, Ijemploy Aa serles of oscillation sources,selected ones ott which are shown in FIGURE 5a and designated by lC., C41? etc.the remaining sources of the chromatic, equallytemperedscale being omitted to simplify the diagram. 'Since it necessary to have 18 generators tuned to the consecutive-half tones above the highest note upon which a chonus effect is to be produced, it is convenient to designate this group, of generators las a Ifirst group, andIk they have been illustrated lragmentarily at 60a inFIGURES 5o and 5b. I-n korder to make use of the chorus effect achieved by the notes of group 60a, there must be at least 12 additional generators tuned to .the consecutive half tones: below the lowest note of the nist group, and these have been ,fragrnentarily shown at 6017 in FIGURE 5a. Also, inthe Kocklmannenl direct oscillations 'from these sources 7through respective decoupling resistors 58 and `59gar1d through key'switches I61, `all switches lloreachkey ofthe ,keyboard preferably being ganged for simultaneous actuation, to be collected by the 2ft., 4 ft. and 8 it. headers designatedlas 2', 4' and 8', respectively, However, theright-hand two switches in each gang shown in FIGURES 5a and Sb'as 61, accord'-v the lower and upper oscillations, respectively, of any` pair selected at the keyboard through the switches 61. Similarly, collectors 6-7 and y69 collect a'll Clt and Gil oscillations which are the lower and upper, respectively, of a pair selected yat the keyboard. In a similar man-ner, oscillations corresponding to the remaining octaves of ten half-tones of the scale are keyed and collected from the remaining sources (not shown) in the instrument.

Celeste tone color In accordance with the principles set `lforth in FIGURE 2 and the desciption of it, I may direct the oscillations collected by collectors such as `63 and '65 through low*- pass electric iilters 71 and 73, if desired for reasons pointed out above with reference to FIGURE 4, of any suitable type `known in the art, to a square-law modulator 75. Similarly, oscillations collected by collectors 67 and -69 may be fed through low-pass lters 77 Iand 79 to a similar modulator 811. Similarly the remaining collectors needed to complete an instrument, feed oscillations through filters yand to modulators, respectively. Thel low- -pass lilters 71, 73, 77 'and 79 etc. will have characteristics such as to limit higher harmonics of an upper-sideband product to levels necessary dor bringing any undesired harmonic effect (explained above) to a negligible point. The modulators 75, 81, etc.` may be of any suitable type known in the |art and may be of the balanced type, arranged so as to produce outputs containing only the lower frequency input oscillations and sum and difference frequencies of the input oscillations. If, however, .for the reasons mentioned above in connection with FIGURE ',7, I use single-sideband modulators of any suitable type, examples of which are shown in U.S. Patent No. 2,248,250, no low-pass Ifilters are necessary.

'Ihe outputs of the respective modulators 75, 81, etc. (FIGURE 5b) are collected by -a bus 83 and fed through a decoupling resistor 84 to a tone-color filter 85, il desired, rlior modicat-ion of harmonic content `in the manner described by Kock in the aforementioned Patent No. 2,233,948, through a stop switch 93 to output bus 95. Similar to the manner set `forth yaboveV in connection with FIGURE 3, oscillations collected by the 8' header are directed through a decoupling resistor S6 `and may be linearly combi-ned at 87 as indicated by the dashed line 87a with the output of the modulators 75, `8-1, etc. to obtain the pairs of two distinct frequencies necessary for the celeste eifcct. Preferably, however, I pass the output of the 8 head-er through suitable decoupling resistors. 86 and 88 to a separate 8 tone-color lilter 89 (without the connection 87a to point 87) and switch 91, ganged with stop switch 93, employed yfor connecting the output of the 'lilter 85 to output bus 9S. l

In the usual manner I may direct the output of the bus 95 through an ampliler system 97 and electroacoustic system 99. Volume control means (not shown) may also be employed in the usual manner in conjunction Ywith the amplifier 97, as desired.

'In accordance with the teachings made in conjunction with FIGURE 4, I may prefer to employ that variation in the system of FIGURES 5a and 5b which is shown in FIGURE -6, in which the output of the 8' celeste tonecolor til-ter S5 is directed via a separate amplifier 94 to a separate electroacoustic system 96.

Nuzard and mixture tone colors According to another 4aspectof my invention, I have at my disposal, by means of the circuits described above and These oscillations yare respectively |fed to pairs' 1 1 shown in FIGURES 5a and Sb-and without ladding any more .generators and key'switches--the necessary voltages tq'provide a .nazard-tone color .(an octave plus a temperedfth above -the Ifoundation tone which, in this case,

isf'an 8' tone), a three-rank mixture (three differentV footages sounding simultaneously from a given stop) and either of two two-rank mixtures'. The nazard tone color can lbe made available by collecting in a bus 101, through -a plurality of decoupling resistors .103, the voltages keyed into a plurality of collectors 65, l69, etc. It will beobvious by inspection ofthe diagram in FIGURES 5a and 5b that when any given key-switch `61 is closed, the yfundamental frequency component of the voltage transmitted tothe bus "101 will Ialways be la twelfth (an octave plus a fifth) above that keyed into the 8' header. A nazard tone color iilter 102, is preferably usedto modify as desired, the `harmonic content of the output of the bus I101, a switch 104 being provided as shown for selecting the hazard-voice. A decoupling resistor 106 maybe used, as shown, in the usual manner.

A three-rank mixture can be obtained by combining through a plurality of decoupling resistors 105, 107, and 109 the voltages present on the 2 header, the 4' header, and the bus 101, respectively. The combination may be passed with or without iilter'ing, as desired, through a tone-color circuit 11.1 and a stop switch 113 to the output but 95. Alternately I may pass the outputs of the bus 101 andthe 2' and 4 headers through separate tone-color circuits and ganged stop-switches (not shown) to the output bus 95.

Regular tone colors In thev Kock manner, I may provide standard 2', 4', and 8 tone-colors as'shown in FIGURES 5a and 5b, by passage of the outputs of the 2', 4' and 8 headers through decoupling resistors 108, 110 and y112, through respective 2', 4 and 8 tonecolor circuits (designated further as 2 T.C., 4 T.C., and 8 T.C., respectively) and stop switches as shown, to the output bus 95.

32 ft. and quin! tone colors `generators,. which, it will be understood may, if desired,

'be' the same ones yas those of FIGURES Sarand 5b, if a completeinstrument with manual and pedal keyboards lis sought. 'Ihe generators or sources are designated as Cz, C2i?, etc., similar to the case of FIGURES 5a and 5b,

' -and in the usual complete instrument, comprise Isa` i chromatic equally-tempered scale of 5 or 6 octaves.

' Through suitable decoupling resistors 115 and key switches 117, are 'passed oscillations from these sources, iso as to provide 16 oscilaltions to a 16 header, 16 oscillations to a collector, such as that designated as 119, and 10i/s oscillations (corresponding toa note a tempered fifth above the 16 oscillation) to a collector such as 121. T65

lSimilarly, oscillations from other sources are supplied (as shown in FIGJS) to the remaining collectors 123, 125, etc.

A'Inga manner similar to the example of FIGURES 5a `and-5b, the twelve collectors 119, 123, etc. of FIGURES feed-into twelve square-law modulators, only one (designated as 127) of which is shown n the interests of simpli` fication of the diagram. Connections from the twelve collectors .1241, `125, etc.,v are made to the respective modulators 127, etc., las at129. Thus, the outputs of the modulators such as 127 will contain oscillations 12 which have, as'inj thecase of FIGURES 5a and 5b, a diierencefrequency component which is nearly an octave below thatl of thel' oscillations Apresent in the 16' header. The bus 131 collects the respective output from the twelve modulators for modification as desired by a tone-color filter such as 32' T.C. In the usual manner a switch 133 may connect the filter output to the output bus `135v for amplification, Volume control and conversion to sound in the amplifier 137 and loudspeaker system 139. Similar to the example of FIGURES 5a and 5 b, a 102/3 or quint tone-color is available inthe circuitof FIGURE 8 by directing the output of the respective collectors 121, 125, etc., collected by the bus 141, to an appropriate filter 143 for modication of harmonic content if and as desired. A stop-switch 145 connects the quint to the output but 135 for conversion to sound. In the usual manner, 16 tone-colors can be obtained by connecting one or more 16' lters, such as 147, for example, to the A16' header, for transmission as 4shown in FIGURE 8 to the output system 139 via stop switch 149.

It will be understood that I am not limited to any specific musical intervals as to the oscillations combined. Though the tempered fifth is thenexemplary interval, it will be obvious that other intervals, such as the tempered fourth, referred to above, may be employed. In the case of the fourth, if, for example, C4 (261.626 c.p.s.) and F4 (349.228 c.p.s.) are combined in the manner of my invention, the derived tone will be at 87.602 c.p.s. which is .295 c.p.s. different from F2 (87.307 c.p.s.) which is two octaves below F4. To obtain a celeste effect, then, acording tc my invention, the F2 (derived voltage) would be combined algebraically with an F2 voltage. It will be understood that low-pitched notes and mixtures will be also available from the use of fourths and other suitable intervals in accordance with the basic teachings herein.

While for the purpose of illustrating and describing the present invention particular embodiments have been shown in the circuit diagrams of the drawings, it is to be understood that the invention is not limited thereby since such variations in the circuit arrangement employed are contemplated as may be commensurate with the spirit and scope of the invention set forth in the accompanying claims.

I claim as my invention:V l

1. An electrical musical instrument comprising a set of audio-frequency sources of electric oscillations having frequencies corresponding to the tones of an equallytempered scale in which the fundamental frequency of each tone is the twelfth root of two times that of the next lower tone, said sources consisting of a rst group lof 19 generators tuned to the frequencies of consecutive half-tones and a second group of at least l2 generators Vtuned to the frequencies of the consecutive half-tones immediately below the "first group, a keyboard having keys corresponding to said tones, at least three switches mechanically coupled' to each key, the rst of 4said switches being coupled to a first source included in the second group of sources corresponding to the normal tone pitch of the key, the second ofsaid switches being coupled to a second source tuned'to a frequency an octave above said rst source, and the third of said switches being Vfor electrically connectingthe first switch of each key and the output of each modulator to the electroacoustic translating means including switch means selectively associating the outputs of 'said Imodulators with the electroracoustic translating system" 2l The combination claimed in claim 1 including circuit means having a stop switch operatively associating the firstswitch of each octavely related key with said electroacoustic translating system.

3. The combination claimed in claim 1 including circuit means having a stop switch operatively associating the iirst switch of each octavely related key to a second electroacoustic translating system.

4. The combination claimed in claim 2 including another stop switch selectively coupling said second plurality of collectors directly to said electroacoustic translating system to provide a tone-color a twelfth above the normal pitch for each key.

5. The combination claimed in claim 1 including a fourth switch for each key of said keyboard, circuit means operatively associating said fourth switch with one of said sources to select voltage components from said sources each of which is harmonically related in frequency to the normal pitch for the key, and circuit means including a manually operable stop switch selectively coupling to the electroacoustic translating system the algebraic sum of the voltages collected by said second set of collectors and said circuit means associated with the fourth set of switches, thereby to provide a mixture tone-color.

6. The combination claimed in claim 3 including another stop switch selectively coupling said second plurality of collectors directly to an electroacoustic translating system to provide a tone-color a twelfth above the normal pitch for each key.

7. The combination claimed in claim l including a fourth switch for each key of said keyboard, circuit means operatively associating said fourth switch with one of said sources to select voltage components from said sources each of which is harmonically related in frequency to the normal pitch for the key, and circuit means including a manually operable stop switch selectively coupling to another electroacoustic translating system the algebraic sum of the voltages collected by said second set of collectors, and said circuit means associated with the fourth set of switches, thereby to provide a mixture tone-color.

8. In an electronic musical instrument comprising two sources of audio frequency substantially a tempered interval apart, modulating means operatively associated with said sources to produce a frequency slightly below that of a harmonically related tone below the lower of said sources, a third audio frequency source having a frequency harmonically related to the lower of said two sources and slightly higher than the produced frequency, and means operatively associated with the modulating means and the third source for simultaneously converting the produced frequency and the frequency ofthe third source to sound.

9. A musical instrument comprising the elements of claim 8 wherein the means for simultaneously converting the produced frequency and the frequency of the third generator to sound comprises an electroacoustical devicel having an input circuit electrically connected tothe modulatin g means and to the third source.

l0. A musical instrument comprising the elements of claim 8 wherein the means for simultaneously converting the produced frequency and frequency of the third source to sound comprises a first electroacoustical device having an input circuit connected to the modulating means, and a second electroacoustical device having an input circuit connected to the third source. x,

1l. An electronic musical instrument comprising the elements of claim 8 wherein the modulating means comprises a square law modulator.

l2. An electric musical instrument comprising a first group of nineteen generators of periodically varying voltages tuned to the frequency of the consecutive half tones of the equally tempered scale, -a second group of at least twelve generators of periodically varying voltages tuned to the frequency of the consecutive half tones immediately lower in'frequency than the first group of generators, a square law modulator having a first input cir- 14 cuit connected to each of the generators in the first group and each of the generators of the second group higher in frequency than the twelve. lowest frequency generators, each of said modulators having a secondY input circuit electrically connected to the generator tuned seven half tones lower in frequency, and means electrically connecting the output of the modulator to the generator of the second group having a frequency twelve half tones below the frequency of said latter generator.

'13. An electronic musical instrument `comprising a first group of nineteen generators of periodically varying voltages tuned to the frequency of the consecutive half tones of the equally tempered scale, a second group of at least twelve generators of periodically varying voltages tuned to the frequency of the consecutive half tones immediately lower in frequency than the first group of generators, each generator of the lirst group and each generator of the second group higher in frequency than the twelfth lowest frequency generator of said group being connected to electrical mixing means, each electrical mixing means being electrically connected to the generator having a frequency a fifth higher than the generator connected thereto, said mixing means producing a frequency slightly below that of the source an octave below the frequency of the lower of said generators, and means for converting the pro-duced frequency and the frequency of the generator an octave below the lower frequency source connected to the mixing means to sound.

14. A musical instrument comprising the elements of claim 13 wherein the means for converting the frequency produced to sound comprises an electroacoustical device electrically connected to the mixing means and to the generator having a frequency an octave below the lower of the generators connected to the mixing means.

l5. A musical instrument comprising the elements of claim 13 wherein the means for converting the frequency produced to sound comprises an electroacoustical device electrically connected to the mixing means, and a second electroacoustical device electrically connected to the generator having a frequency an octave below the lower of the generators connected to the mixing means.

16.1In an electronic musical instrument comprising two sources of audio frequency substantially a tempered interval apart, modulating means operatively associated with said sources to produce a frequency of slightly different frequency than the tone harmonically related to one of the sources, a third audio frequency source having a frequency corresponding to said tone of the equally tempered scale harmonically related to one of the two sources and slightly different in frequency than the produced frequency, and electroacoustical means associated with said modulating means and the third audio frequency source to convert the produced frequency and third source to sound simultaneously.

17. An electrical musical instrument comprising a set of sources of electric oscillations Yhaving frequencies corresponding to the tones of the equally tempered scale in which the fundamental frequency of each tone is the twelfth root of two times that of the next lower tone, said sources consisting of a first group of nineteen generators tuned to the frequencies of consecutive half-tones and a second group of at least twelve generators tuned to the frequencies of the consecutive half-tones immediately below the first group, a keyboard having keys corresponding to each half-tone, at least three switches mechanically coupled to each key, the first of said switches being coupled to a first source included in the second group of sources corresponding to the normal tone pitch of the key, the second of said switches being coupled to a second source tuned to a frequency an octave above said first source, and the third of said switches being coupled to a third source a tempered fifth above the second source, a modulator associated with each key having inputs electrically connected to the second and third switches of said key, and an electroacoustic translating means electrically connected to the vrst switch of each key and the output of each modulator. t

References rCited in the le of this patent Y UNITED STATES PATENTS 5 Hammond May 23, 1939 Bergen et al. July 9, `1940 Hammond et al Feb. 21, 1950 Haller et al. Apr. 25, 1950 10 France Feb. 20, 1939 

